Unnamed Occurrences (ARDF - CR024), Black Bear Lake, Prince of Wales Island, Ketchikan Mining District, Prince of Wales-Hyder Census Area, Alaska, USAi

Regional Level Types
Unnamed Occurrences (ARDF - CR024)	Group of Occurrences
Black Bear Lake	Lake
Prince of Wales Island	Island
Ketchikan Mining District	Mining District
Prince of Wales-Hyder Census Area	Census Area
Alaska	State
USA	Country

Location: This occurrence is at an elevation of about 500 feet, about 0.7 mile north-northwest of the outlet of Black Bear Lake. It is near the center of the SW1/4 section 1, T. 73 S., R. 82 E. This site includes another occurrence about 0.2 mile to the south in a quarry shown by symbol on the USGS 1:63,360-scale topographic map; it is about 0.5 mile south-southwest of the center of section 1, T. 73 S., R. 82 E.
Geology: This occurrence, discovered in 1988, is what was originally interpreted as a vertical, roughly elliptical, breccia pipe about 600 feet long and 300 feet wide (Hedderly-Smith and Glavinovich, 1991; Maas and others, 1991; Hedderly-Smith, 1999 [Inventory]). Later work by Hedderly-Smith indicates that the occurrence may not be a vertical pipe but instead is a northeast-trending breccia zone along a fault. The occurrence is at or near the contact between a Cretaceous granitic pluton and metamorphosed volcanic and sedimentary rocks of the Luck Creek Breccia of Silurian and Ordovician age (Eberlein and others, 1983; Brew, 1996). The breccia is composed of intensely altered clasts of diorite in a quartz-pyrite matrix; the breccia contains minor chalcopyrite and molybdenite. Three samples collected by Hedderly-Smith (1991) contained up to 0.07 percent copper, 0.064 percent molybdenum, 0.06 percent tungsten, and 0.03 ounce of gold per ton. Samples taken by Maas and others (1991) of material with masses of pyrite up to 6 inches across contained up to 23 parts per billion gold, 2.5 parts per million (ppm) silver, 0.53 percent copper, and 101 ppm molybdenum. Aerial photographs indicate that several arcuate structures surround the breccia. Ground geophysical surveys show that the electric response of the breccia is weak, but show an anomalous zone downslope from the breccia.
Workings: Only surface sampling by geologists from government and private industry.
Age: The breccia is probably related to the contact of a Cretaceous granitic pluton.
Alteration: The diorite clasts in the breccia are intensely altered.

Commodities (Major) - Ag, Au, Cu, Mo; (Minor) - W
Development Status: None
Deposit Model: Breccia zone with chalcopyrite and molybdenite.

Other Databases

Link to USGS - Alaska:	CR024

Other Regions, Features and Areas containing this locality

References